1. Field of the Invention
The present invention relates to an image recording method wherein an image is recorded by electrochemically depositing an image forming material using an aqueous liquid containing fine particles of a coloring material.
2. Description of the Related Art
Many methods of using a liquid image forming material are known in image recording technologies used in offices. For example, silver salt recording technology, ink jet recording technology, and electrophotographic recording technology.
Printing technology using silver salt has been published in Tanemura Hatsumi et al., "HIGH QUALITY COLOR COPYING SYSTEM BY SILVER SALT PHOTOGRAPHIC METHOD", Preprint of Japan Hardcopy '89, p229. Printing technology using liquid development electrophotographic technology has been published in E. B. Caruthers et al., "Modeling of Liquid Toner Electrical Characteristics", Proceedings of IS & T 10.sup.th Int'l. Congress on Advances in Non-Impact Printing Technologies, p204 ('94). Printing technology using ink jet recording has been published in many technical reports such as Usui Minoru, "Development of a New Process MACH", Preprint of Japan Hardcopy '96, p161.
There are also proposed, for example, a technology using an electrodepositable liquid in which a coloring material is dispersed in an electrically insulating liquid so as to generate an electrical double layer (Japanese Patent Application Laid-Open (JP-A) No. 7-181750 or Japanese Patent Application Publication (JP-B) No. 7-54407); "Fine Pattern Forming Method" relating to an electrodeposition printing technology using a printing plate comprising an electrically conductive substrate with an insulating pattern formed thereon (JP-A No. 4-9902); and "Electrodeposition Offset Printing Method and Printing Plate" (JP-A No. 6-293125).
Properties required for printing technology for use in offices are, for example, a color high-quality image of 600 DPI (dots per inch) or higher and multi-gradation, capability of printing on plain paper, high image fastness comparable to that of a printed product, high safety of the recorded matter and the recording apparatus, almost no waste produced, and low running cost. However, none of the conventional technologies have reached the level at which the above-mentioned requirements are completely satisfied.
The recording method using silver salt, which is one of the conventional printing technologies, does not present problems of image quality or image fastness. However, the use of this method in an office is associated with problems, because this method is based on a printing process which involves a chemical reaction using chemically active agents and producing waste. The problems of ink jet printing technology are that high resolution cannot be easily obtained because of problems created by the small nozzle diameter in printing reliability; and that image fastness, safety, and printability on plain paper are inadequate, because the image forming material is usually an aqueous dye. Electrophotographic technology has no problem with regard to image quality, printability on plain paper, and high image fastness comparable to that of a printed product. However, electrophotographic technology has the disadvantages that a large amount of energy is consumed in the fixing unit of an electrophotographic apparatus; that the size of the apparatus is large because of the complicated printing process; and that safety and reliability problems arise.
In order to obtain an image having a high quality (resolution of a level of 1000 DPI, good color reproduction, and multi-gradation), the thickness of the image structure is preferably 2 microns or less, and more preferably 1 micron or less, in the light of the relationship between the range of color reproduction and the sharpness of image. Accordingly, the average particle size of the image forming material, as the element which imparts structure to the image, needs to be of a sub-micron order. However, since a fluidity problem arises if the average particle size of the image forming material is 5 .mu.m or less, practical use of a powdery image forming material is difficult. In comparison , when viewed from this standpoint, the use of a liquid image forming material would be effective. In the step of forming an image having a size of the order of several microns, it is technically difficult to accurately control the movement of the particles of image forming material if the size of the particles is very small. Accordingly, an image forming method, in which an image is formed by using the electrophoresis of fine particles through a liquid, enables the accurate control of the movement of the particles and therefore is considered to be a very effective technical method.
The electrophotographic technology, which uses a developer in the form of an electrically insulating liquid and which is disclosed in, for example, JP-A No. 7-181750, is advantageous in that high resolution can be obtained because the size of the image forming material is of a sub-micron order; and in that image transfer can be easily performed at room temperature and printability on plain paper is high because the image formed can be altered while it is wet. However, since this method uses a developer comprising a hydrocarbon solvent, the solvent vapor presents a serious safety problem. Therefore, the use of such a developer is strictly regulated in some countries.
The electrodeposition printing technology using a printing plate comprising an electrically conductive substrate and an electrically insulating pattern formed thereon as described in JP-A No. 4-9902 is disadvantageous in that it is difficult to change image patterns for each printing because the process is complicated, for example, the non-image portion of an insulating resist needs to be prepared beforehand by photolithography. Other disadvantages are as follows. Since the apparatus to be used in this method is provided with a high precision, has a large size, involves many steps and produces a large amount of waste, it necessarily follows that the place where the apparatus is installed for printing is limited to a factory well equipped with facilities. Further, since the hysteresis of the image forming step tends to remain on the substrate, minute image recording cannot be fully reproduced. Furthermore, since the image forming portions in this method are concave, it is difficult to obtain a high quality image, because the selective adherence of particles to the image portions by electrophoresis is weakened and a large proportion of the liquid component of the image forming liquid material tends to remain on the image forming portions thus reducing the viscosity of the image forming material in the image forming portions, and consequently the image forming material in the image forming portions is liable to flow or cause a cohesive failure in the transfer step.
As described above, technologies of conventional image forming methods cannot satisfy the properties, i.e., a high degree of safety using a simple apparatus, required for printing for use in offices.